Age effects on neurochemical markers and the correlation between brain neurochemical markers and motor performance were tested in C57BL/6J and A/J mice. Motor performance was altered by age, and age effects varied with genetic strain. Age-associated decrements in performance were correlated with regional changes in cholinergic, GABAergic, and catecholaminergic neurochemical markers. Activities of choline acetyltransferase (CAT), glutamic acid decarboxylase (GAD), and tyrosine hydroxylase (TH) were assayed in four brain regions after animals were evaluated in a battery of psychomotor tests. Significant correlations between enzyme activity and motor performance occurred most frequently in the youngest (4-mo) and oldest (24-mo) groups. Examination of age effects on the cholinergic markers, CAT activity and muscarinic binding in C57BL/6J mice revealed regional increases in CAT activity that were associated with increases in Vmax, and no changes in Km. In the cerebral cortex and striatum, these increases in Vmax were associated with decreases in the muscarinic binding sites.